Method for identifying defects in a film, method and device for producing a film

Abstract

A method of identifying a defect in a wet film comprises conveying said wet film (20), in a wet state, on a conveyor (10), providing a laser projection (1511) onto the wet film, acquiring a series of images, each depicting an area of the wet film, wherein at least a portion of the laser projection is visible, and using at least some of said images to identify said defect. There is also disclosed a method and device for producing a film.

1 . A method of identifying a defect in a wet film, comprising:
 conveying said wet film, in a wet state, on a conveyor,   providing a laser projection onto the wet film,   acquiring a series of images, each depicting an area of the wet film, wherein at least a portion of the laser projection is visible, and   using at least some of said images to identify said defect.   
     
     
         2 . The method as claimed in  claim 1 , wherein the laser projection extends across a wet film edge, and wherein said images also depict a portion of an exposed conveyor surface. 
     
     
         3 . The method as claimed in  claim 2 , wherein a wet film thickness is determined as a difference between a measured distance to a conveyor surface laterally outside the wet film and a measured distance to a wet film surface. 
     
     
         4 . The method as claimed in  claim 2 , wherein an average wet film thickness is determined as a difference between a measured distance to a conveyor surface laterally outside the wet film and a plurality of measured distances to a wet film surface within the wet film width. 
     
     
         5 . The method as claimed in  claim 1 , wherein the wet film comprises a film forming component which is distributed in a medium that is to be essentially removed, wherein a content of the medium of the wet film is at least 75% by weight. 
     
     
         6 . The method as claimed in  claim 1 , wherein the wet film is a cellulose based film. 
     
     
         7 . The method as claimed in  claim 1 , wherein the laser projection is applied between a casting device and a first drying device. 
     
     
         8 . The method as claimed in  claim 1 , wherein the laser projection is applied at a position along a forward direction of the conveyor, where a belt support is arranged. 
     
     
         9 . The method as claimed in  claim 1 , wherein the conveyor is a metal belt conveyor a polymer conveyor, or a paper conveyor. 
     
     
         10 . The method as claimed in  claim 1 , wherein the conveyor extends laterally beyond the wet film edge at both lateral sides of the wet film. 
     
     
         11 . The method as claimed in  claim 1 , wherein the laser projection is applied as a fixed pattern, or wherein the laser is scanned with a frequency that is greater than an image capture frequency so as to effectively present a pattern. 
     
     
         12 . The method as claimed in  claim 1 , wherein the laser projection is applied from a laser direction which extends at an angle to a direction of travel of the conveyor, and in a vertical plane containing said direction of travel, said angle being between 5-80 degrees. 
     
     
         13 . The method as claimed in  claim 1 , wherein the laser projection is applied from a laser direction which extends at an angle to a direction of travel of the conveyor, and in a vertical plane containing said direction of travel, said angle being between 100-175 degrees. 
     
     
         14 . The method as claimed in  claim 12 , wherein the images are captured such that an image plane of the image capture device is perpendicular to a line that extends in a vertical plane and at an angle of between 30-150 degrees to the laser direction. 
     
     
         15 . The method as claimed in  claim 12 , wherein said defect is identified by comparing an actual pattern provided by the laser projection, as derived based on said images, with an expected pattern. 
     
     
         16 . A method of producing a film, comprising:
 providing a continuous conveyor having a conveyor width,   using a casting device for applying a film comprising a film forming component which is distributed in a medium that is to be essentially removed onto the conveyor, so as to solvent cast the film,   identifying a defect in the wet film according to the method as claimed in  claim 1 , and   providing an indication of said defect.   
     
     
         17 . The method as claimed in  claim 16 , further comprising adjusting at least one casting parameter based on said indication, or based on said images, or based on both. 
     
     
         18 . The method as claimed in  claim 17 , wherein adjusting at least one casting parameter comprises adjusting a wet film feed rate, or a feed distribution, or both. 
     
     
         19 . The method as claimed in  claim 17 , wherein adjusting at least one casting parameter comprises adjusting a doctor blade, which is configured for controlling a wet film thickness, a wet film thickness distribution, or both. 
     
     
         20 . The method as claimed in  claim 17 , wherein adjusting at least one casting parameter comprises adjusting a lip of a slot die type casting unit. 
     
     
         21 . The method as claimed in  claim 16 , further comprising at least one of:
 providing an alarm directed to an operator,   recording a position corresponding to the defect, and   stopping at least one of the casting device and the conveyor.   
     
     
         22 . A device for producing a film, comprising:
 a continuous conveyor having a conveyor width,   a casting device for applying a wet film comprising a film forming component which is distributed in a medium that is to be essentially removed onto the conveyor, for solvent casting the film to provide a wet film width that is less than the conveyor width,   a laser projection device configured to provide a laser projection onto the wet film,   an image capture device, configured to acquire a series of images, each depicting an area of the wet film, wherein at least a portion of the laser projection is visible, and   a processing device, configured to use at least some of said images to identify a defect in the wet film.   
     
     
         23 . The device as claimed in  claim 22 , further comprising an adjustable device, configured for adjusting the casting device based on said identified defect in the wet film. 
     
     
         24 . The method as claimed in  claim 1 , wherein the wet film is a microfibrillated cellulose film.